1. Field of the Invention
The present invention relates generally to video data processing techniques and specifically to a unique method and apparatus for merging internal stored or generated video with external video and for processing a resultant video for use in a projection display system.
2. Discussion of Prior Art
The projection of computer generated images through use of liquid crystal display panels is well known in the art. See for example, Vogeley et al, U.S. Pat. No. 4,976,536, issued on Dec. 11, 1990 and U.S. Pat. No. 4,763,993, issued Aug. 16, 1988 and other patents cited therein. It is noted that video input signals can include a wide variety of input formats including VGA, EGA, CGA, Mac II, and a variety of other computer generated video signals, as well as real time motion video signals including NTSC, PAL, SECAM, and that provided by various VCR players are also available.
These videos are clocked at a wide variety of frequencies and are in many different formats. It is sometimes required or desired that these videos be reformatted (double scanned, etc.), as discussed in U.S. patent application Ser. No. 07/664,950, filed Mar. 5, 1991, entitled "Method and Apparatus for Displaying RGB and Sync Video Without Auxiliary Frame Storage Memory", also by Vogeley et al.
In providing video signals for projection, either by projection television techniques or more preferably, by supply to a liquid crystal display (LCD) equipped projector, it is also desirable to provide independently generated video images. In the past, such internally generated images were either merged with the external video source (overwritten) or independently viewed. Such internal video images might be a menu, graphics or an actual video image retrieved from a local mass storage device such as a ROM or disc drive. While not essential, it is desired that the internal video be independent of processing applied to external video signals (panning, reformatting, zooming, etcetera).
Generally LCD displays are clocked at a constant clock frequency which may be dramatically different from the clock frequency of the external video input or even an internally generated signal. Although video is generally projected directly upon a screen, it is also desirable to be able to provide an image reversal or a "mirror image" such that the video can be applied to a rear projection screen for front viewing. As previously noted, depending upon the LCD display chosen, the display clock frequency may vary from 30 hertz vertical frame rate up to 100 hertz or higher.
With regard to external and internal video, it is also desirable to be able to "zoom" or provide a magnified image of a limited portion of the complete video image and then to be able to "pan" the "zoomed" image to that specific portion of the nonzoomed image which was of interest. Although generally image panning is associated with only a zoomed image, it is also desirable to be able to pan a non-zoomed image so as to move a portion of an unzoomed image off of the screen, perhaps making room for a blanked-out portion of the screen suitable for writing in operator control video such as is described in U.S. application Ser. No. 07/698,091, "Method and Apparatus for Interacting With a Computer Generated Projected Image", filed May 10, 1991, also by Vogeley et al.
While the above aspects of a video projection system are desirable, other than by means of a simple overwriting technique which permits user prompts or company logo displays, applicants know of no LCD projection apparatus which can provide a combination of external and internal video (in the manner of "windows" utilized in computer software systems), zooming, panning, or reverse images for external or internal video whether reformatted or not. The advanced capabilities, such as internally generated graphics generation and/or image retrieval, that are entirely independent of a wide variety of incoming video signals, including both computer generated video and real time video, that can be overlayed or merged with incoming video and can be randomly edited has never been previously accomplished to the inventor's knowledge.